The invention relates to a vertical heat treatment device for semiconductors. A plurality of semiconductor wafers are horizontally placed on the device at intervals in a vertical direction for heat treatment, for instance, forming a silicon oxide film on the surface of each wafer and diffusing impure atoms therein. This device is also called a vertical boat.
This type of vertical heat treatment device for semiconductors is known. Japanese utility Model laid-open No. 62-128633, for example, shows a device as shown in FIGS. 7 and 8.
The conventional vertical heat treatment device shown in FIGS. 7 and 8 comprises two end plates 60 located at the top and the bottom of the device, four support bars 70 vertically mounted on the end plates 60 at intervals, and a plurality of wafer hold members 80 mounted on the support bars 70 at vertical intervals G. The wafer hold member 80 has an approximately half-circular ring shape in plan view and has the same radius of curvature as that of the semiconductor wafer W. The wafer hold member 80 is fixed circumferentially at four spots to the support bars 70 as shown in FIG. 7. An upper portion of the support bars 70 is not shown.
The wafer hold member 80 has a circular arc channel or groove 81 formed inside the top surface thereof, as shown in FIG. 8. The bottom surface of the groove 81 is a wafer placing surface 82 on which the Wafer W is to be placed whereas the side surface of the groove is a wafer engaging surface 83 with which the periphery of the wafer W is to be engaged. The wafer W is transferred by the arm of a transfer robot in the vicinity of the device 50 and placed on the wafer placing surface 82 through the cutout of the wafer hold members 80. The wafer is positioned in such a manner that its circumference is engaged with the wafer engaging surface 83. A wafer place portion 84 including the wafer placing surface 82 has a thickness of T.
The wafer hold member 80 is formed by a silica glass single body, a SiC single body impregnated with Si, a SiC base body impregnated with Si having a CVD-SiC film coated thereon, a carbon base body having a CVD-SiC film coated thereon, or the like.
In said conventional vertical heat treatment device for semiconductors, the wafer place portion 84 of the wafer hold member 80 has a significant thickness T, for instance larger than 1000 microns, for obtaining an enough strength, thereby it has a large heat capacity. Therefore the wafer W held thereon can hardly be heated in the predetermined temperature pattern. As the result, the time required for heat treatments will be increased and characteristics of the wafer surface will be uneven.
As far as each wafer W is concerned, the temperature rises at a more slow pace in the circumferential area engaging with the wafer hold member 80 than in the other areas. Therefore a considerable temperature difference between the two areas is caused, resulting in uneven characteristics of the wafer surface.